The present disclosure generally relates to a gas chromatograph. More particularly, the disclosure relates to a multilayered gas chromatograph with which sample analyses can be conducted quickly with minimal down time between analysis cycles.
Gas chromatography is a field concerned with analyzing samples of interest, which may include one or more analytes, to qualitatively determine the identity of the analytes as well as to quantitatively determine the concentration of each of the analytes in the sample. Gas chromatography is extremely sensitive and therefore is normally used where very precise analysis of a sample is required. The analysis can comprise the identification of the various individual analytes, or comparison of the entire sample response (e.g., chromatogram) to previously analyzed samples for the purpose of classifying the sample.
Gas chromatography typically involves separation of the analytes of a sample material through use of a gas chromatograph. Normally, gas chromatographs comprise an inlet in which the sample is injected, a column in which the analytes are separated, and a detector in which the various analytes are detected and, if desired, quantitatively evaluated. The column usually is made from fused silica that is formed into a narrow, elongated tube. By way of example, the chromatograph column can have an inner diameter on the order of approximately 50 to 530 microns (xcexcm), and a length of approximately 1 to 30 meters. To decrease the size of the chromatograph apparatus, the column normally is arranged in a coiled configuration. By way of example, the coil can have a diameter of approximately 8 inches (in) such that the column can be packaged, for instance, in a cubic foot of space.
The interior walls of the gas chromatograph column are coated with a material commonly referred to as a stationary phase. The stationary phase retains the various analytes of the injected sample and, through the application of heat, releases the analytes so that they are received by the detector separated in time. Through knowledge of the temperature of the column and the duration of time that passes between injection and detection, the individual analytes passing through the detector can be identified.
As is known in the art, heavier compounds require more heat and/or more time to elute from the column than do lighter compounds. For instance, at a relatively low temperature (e.g., at 100xc2x0 C.), the lighter analytes may elute from the column stationary phase after only a few seconds while the heavier analytes may require many minutes or even hours to separate. Therefore, it can be appreciated that the greater the heat, the faster the heavier analytes can be eluted from the column. Where the sample is complex, however, for instance having several light and heavy components, high temperatures (e.g., 300xc2x0 C.) cause the lighter analytes to immediately elute such that many different analytes arrive at the detector simultaneously. This simultaneous arrival complicates the analysis of the sample analytes in that, where the detector is non-selective, the detector cannot distinguish the various analytes from each other. To avoid this problem, gas chromatographs are often heated in a programmed, air-bath oven which increases the temperature of the column at a steady rate (e.g., 20xc2x0 C./minute). By heating the column in this manner, the low temperatures needed for adequate separation of the lighter analytes are provided, as well as the higher temperatures needed to elute the heavier analytes from the column.
Although adequately functional for most sample analysis situations, conventional gas chromatographs present several drawbacks. First, a cool down period normally is needed in between analysis cycles to reduce the temperature of the column from the final temperature to the initial temperature. By way of example, this cool down can require approximately 15 minutes or more. Although not an exceedingly long period of time, this duration is substantial, especially where the samples are being analyzed with xe2x80x9cfastxe2x80x9d chromatography which often only requires a few minutes. In addition to cool down time, time is wasted in permitting the system to achieve equilibrium. As is known in the art, if thermal equilibrium is not achieved prior to conducting a sample analysis, substantial fluctuation in analyte retention times can occur. Furthermore, column bleed fluctuations that occur during over temperature programming can increase the chromatogram baseline noise and/or drift that can mask analyte peaks.
From the foregoing, it can be appreciated that it would be desirable to have a gas chromatograph with which sample analyses can be conducted quickly with minimal down time between analysis cycles.
The present disclosure relates to a gas chromatograph having a plurality of layers or channels. The chromatograph typically comprises an inlet that receives a sample to be analyzed, a column disposed in each of the plurality of chromatograph layers, each column being in fluid communication with and downstream from the inlet and having a stationary phase coating its inner surfaces, and a detector in fluid communication with and downstream from at least one of the columns. In a preferred arrangement, the chromatograph includes a pre-column disposed in each of the chromatograph layers upstream of the columns, each pre-column being in fluid communication with the inlet and having a stationary phase coating its inner surfaces.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.